We propose to assess the genotype-phenotype relation of variants in five genes that synthesize or metabolize 5-methylTHF or homocysteine. The five genes are: MTHFD1 (5,10 methylenetetrahydrofolate dehydrogenase), MTHFR (methylenetetrahydrofolate reductase), MTR (Methionine Synthase), MTRR (Methionine Synthase Reductase), and SAHH (S-adenosylhomocysteine hydrolase). We will explore SNPs or newly defined haplotypes in these genes in relation to plasma folate and homocysteine already assessed among 943 men and women; a population over-sampled to represent a wide range of alcohol consumption.